Conventionally, an ophthalmic lens such as a contact lens or an intraocular lens is provided with an identifying mark in the form of characters such as numbers and alphabets, figures, symbols, etc., principally for easy distinction between the front and back surfaces of the lens or between lenses for the left and right eyes, and/or indicating the specifications and/or maker of the lens, for instance.
Various methods are known for marking the ophthalmic lens with the above-mentioned characters, figures, and symbols. For example, there are known printing methods in which marks are transferred on the lens surface by using dyes or colorants (see, for example, JP-A-4-270312 and JP-A-62-288812), and laser radiation marking methods in which desired marks are printed or engraved by irradiation of a laser radiation (see, for example, JP-A-6-31654 and JP-A-57-210317).
However, for the mark formed by the former printing method, there are concerns that the dyes or colorants of the mark may be flowed off, discolor, or peel off due to various treatments repeatedly conducted on the lens, such as cleaning of the lens by rubbing and repetitive disinfection. Moreover, marking of an ophthalmic lens by the printing method requires many process steps for marking the ophthalmic lens, such as a drying step after the printing, and also requires many devices for the process steps. In addition, the ophthalmic lens needs to be handled frequently, undesirably resulting in a high defect or reject ratio of the ophthalmic lens. Accordingly, the cost of manufacture of the ophthalmic lens is undesirably increased, causing a problem of poor economy.
Meanwhile, the mark formed by the latter laser radiation marking method is not easily readable. In addition, as the mark is made by forming grooves or recesses on the lens surface by the laser radiation, the thickness of the portions of the lens, which are subjected to the laser radiation, is inevitably reduced, or the lens material is denatured by the laser radiation. In either case, the strength of the ophthalmic lens is reduced. Further, deposits are likely to accumulate in the grooves or recesses made by the laser radiation, causing undesirable troubles such as irritation of the eye of the lens user.
JP-A-6-258604 discloses a molding method using a material for transfer printing, in which the material has printing layers including a layer of a pattern. By molding a contact lens in this way, the contact lens with the pattern, whose surface is positioned on the surface of the contact lens without a difference in level, is obtained. As an example for the dye for the layer of the pattern, a rhodamine, which is a fluorescent material, may be used. However, there are also concerns for the contact lens prepared by the above-mentioned method that the dye may be flowed off, or the pattern may be discolored or peeled off, due to cleaning of the lens by rubbing and/or repetitive disinfection.
Therefore, the inventors of the present invention have made various studies to obtain a marking method of an ophthalmic lens to form a clear and easily readable mark, without causing problems such as discoloration of the mark caused by cleaning of the lens by rubbing or deterioration of the mechanical strength of the lens. The studies made by the inventors of the present invention have revealed that if a rhodamine derivative, which exhibits desired coloring effect, is previously added to a predetermined polymerizable composition of monomers for the ophthalmic lens, and then the polymerizable composition of monomers is polymerized, the color of the rhodamine derivative is discolored or faded. The studies have also revealed that if the ophthalmic lens made of the polymer, which is obtained by the above polymerization, is irradiated with a light, the discolored color of the rhodamine derivative is restored at the position where the light is irradiated.